The present invention relates to an electronic earth leakage current device for a low-voltage power line, having improved functionality.
In particular, the present invention relates to an electronic earth leakage current device, for single- or three-phase low-voltage power lines (therefore for voltage values below 1 KV).
Many examples of electronic earth leakage current devices for a low-voltage power line are known.
The main function of an electronic earth leakage current devices is to interrupt the power line if an earth leakage current (or residual earth fault current or imbalance current), above a certain preset threshold, is detected. The power line, on which a tripping event occurs, can be the power supply line (single- or three-phase) related to a specific load or to a local electrical user, for example of the industrial or domestic type.
The expression xe2x80x9cearth leakage currentxe2x80x9d is to be understood as describing, for example, an earth fault current generated by any malfunction of the power line or of the electric loads to which the power line is connected.
For this reason, known electronic devices generally comprise the following functional elements (FIG. 1):
a current sensor 1 for detecting an earth leakage current (also known as imbalance current or residual fault current) in a phase conductor of a power line 5;
an electronic circuit 2 for processing a signal, which is indicative of the earth leakage current, sent by the current sensor 1.
Tripping events, which cause the interruption of the power line, occur, according to universally acknowledged technical standards, which set the technical requirements to be met in order to consider the electronic earth leakage current device safe for the user.
In common practice, a tripping characteristic is determined for each electronic earth leakage current device. This tripping characteristic depends on the constructive characteristics of the device and ultimately on the characteristics of the electronic circuit 2 of FIG. 1.
It is known that the electronic earth leakage current devices of the state of the art have drawbacks.
First of all, known electronic earth leakage current devices are generally not provided with monitoring systems, which allow to easily check the operating condition of the device and to interrupt the power line, if necessary. This can be a source of many problems for the user. For example, a high operating temperature, caused by environmental factors or internal faults, can cause a malfunction of the device, which can compromise its safety.
The absence of monitoring of the voltage level of the power line also can lead to malfunctions of the device and to damage to the electric devices powered by the power line, without having a tripping event.
The operating condition of the device in relation to its connection to the conductors of the power line to which it is connected is also very important.
If monitoring of the connection status of the conductors (neutral or ground or phase) of the power line is not provided, the device may fail to operate due to the interruption of one of said conductors or due to their incorrect connection. In practice, in such situations an earth leakage current in the power line would not trip the earth leakage current device. Accordingly, no protection of any kind would be provided for a user who happened to interact in some way with the power line and/or with the load supplied by said line. This fact entails considerable safety problems, which, at present, can be solved by coupling an electromechanical protection device to the electronic earth leakage current device, with a considerable increase in installation costs.
Furthermore, known earth leakage current devices generally comprise electronic circuits for setting the minimum tripping current and/or the maximum time interval for tripping. These circuits are generally constituted by electronic networks of the RC type, which process the electric signal, which is indicative of the value of the earth leakage current, that arrives from the current sensor. For example, the maximum time interval is commonly set by means of introducing a time delay proportional to the detected earth leakage current value. Although the technical solutions that are commonly adopted allow to preset some important parameters that characterize the tripping criteria of the electronic earth leakage current device, they do not allow to define in advance its overall behavior and therefore the trend of its tripping characteristic. This fact entails a high degree of uncertainty as to the behavior of the device for high earth leakage current values, for which the proportional delay introduced by commonly adopted technical solutions tends to drop to negligible values.
In this manner, there is no longer any control over the tripping times of the electronic earth leakage current device, which substantially depend on the level of wear of the mechanical or electromechanical components of the electronic earth leakage current device. This fact can lead, for example, to unexpected interruptions of the power line that are a severe annoyance for the user. Furthermore, considerable problems can occur if an electric system includes electronic earth leakage current devices in a cascade configuration (for example a device of a general type, connected to a network with selective-type devices). In this case, the uncertainty, related to the minimum tripping time, causes problems in managing the tripping events of the whole network of devices. In addition to this drawback, there is the fact that, since the tripping characteristic is difficult to predetermine, many devices can fail to comply with the standards during testing and inspection. This fact entails, in addition to a high degree of uncertainty as to the compliance of the earth leakage current device to the applicable standards, many difficulties, if it is necessary to meet particular requirements of the electrical user for which the device is intended. For example, it is difficult to determine in advance whether a device must be of the general or selective type or must have a more complex tripping characteristic. Accordingly, complex calibration operations are necessary, in order to achieve a tripping characteristic, which approximates as closely as possible the intended one.
Another drawback arises from the fact that known electronic earth leakage current devices are generally designed to use very specific types of actuator. In practice, the electronic circuits that generate the tripping signal are capable of driving only a certain type of actuator. If one decides to change the type of actuator, then the entire device must be redesigned in order to ensure satisfactory performance.
Another drawback arises from the fact that, in the known electronic earth leakage current devices, the design of the electronic circuits for generating the signal very often takes marginally into account the operating condition of the sensor devices, suitable to detect the presence of an earth leakage current. In particular, technical solutions for monitoring, with diagnostics of the ON/OFF type, the operating condition of the sensor means are very often all that is provided. Since said sensor means have to interface with electronics designed for other specific purposes (the generation of a tripping signal if a certain level of earth leakage current is exceeded), they can find themselves in non-optimum operating conditions, negatively affecting the performance of the entire electronic protection device.
Therefore, the aim of the present invention is to provide an electronic leakage current device for a low-voltage power line, which allows interrupting the power line, if an operating condition that compromises the correct operation of said electronic leakage current device occurs.
Within the scope of this aim, an object of the present invention is to provide an electronic leakage current device, which allows interrupting the power line if its operating temperature exceeds a preset threshold.
Another object of the present invention is to provide an electronic leakage current device, which allows interrupting the power line if the voltage of the power line exceeds a preset threshold.
Another object of the present invention is to provide an electronic leakage current device, which allows interrupting the power line, if an interruption of the neutral and/or ground conductors of the power line occurs or if an incorrect connection of the phase and neutral conductors occurs.
Another object of the present invention is to provide an electronic leakage current device, which allows to easily preset the trend of the tripping characteristic of said device.
Another object of the present invention is to provide an electronic leakage current device, which allows to use several actuation devices without substantial modifications to the electronic circuits suitable to generate the tripping signal for said actuation devices.
Another object of the present invention is to provide an electronic leakage current device, which allows to optimize the operation of the sensors suitable for detecting the earth leakage current.
Another object of the present invention is to provide an electronic leakage current device, which allows to interrupt the power line if the sensors suitable to detect an earth leakage current malfunction.
Another object of the present invention is to provide an electronic leakage current device, which is easy to manufacture and at modest costs.
Thus, the present invention provides an electronic leakage current device for a low-voltage power line, comprising:
a moving contact and a fixed contact which can be mutually coupled/uncoupled; and
first sensor means for detecting a leakage current and for generating an electric signal which is indicative of the value of said earth leakage current; and
first electronic means which are electrically connected to said first sensor means in order to generate, on the basis of said electric signal, which is indicative of the value of said earth leakage current, an electric tripping signal; and
actuation means, operatively connected to said moving contact, in order to perform, in response to command electric signals, the separation of said moving contact from said fixed contact;
The electronic leakage current device, according to the present invention, is characterized in that it comprises:
second sensor means for detecting one or more physical values, which are indicative of the operating condition of said electronic device for protection against earth leakage current; and
second electronic means, electrically connected to said second sensor means, for receiving from said second sensor means electric signals, which are indicative of the operating condition of said electronic leakage current device and for generating said electric tripping signal depending on said electric signals.
The electronic leakage current device, according to the present invention, allows achieving the intended aim and objects. In fact, it ensures, by virtue of the presence of the second sensor means and of the second electronic means, the possibility to detect abnormal operating conditions, which might compromise the safety of the device. In practice, an abnormal operating condition is considered in the same manner as an earth leakage current and produces the tripping of the electronic leakage current device. This forces the user to intervene in safety on the power line or on the electronic device itself in order to restore normal operating conditions.